The invention relates to a circuit arrangement comprising a Cartesian amplifier, including
a signal source for producing an input signal, PA1 a re-combining stage for forming a result signal by re-combining the input signal and a correction signal, PA1 a first mixer stage for mixing the result signal with a first oscillation of the local oscillator, PA1 a power amplifier stage for amplifying the signal produced by the first mixer stage, PA1 a coupler for coupling out part of the output signal of the power amplifier stage as an outcoupling signal, PA1 a feedback path comprising a second mixer stage for deriving the correction signal from the outcoupling signal by mixing the outcoupling signal with a second oscillator of the local oscillator, PA1 an envelope curve detection stage for producing an envelope curve signal which corresponds to the envelope curve of the output signal of the power amplifier stage, PA1 and a phase adjustment stage for adjusting the phase position of at least one of the oscillations of the local oscillator. PA1 a control circuit having
The invention further relates to a transmitter apparatus comprising a circuit arrangement of said type and to mobile radio equipment comprising such a transmitter apparatus.
Such a Cartesian amplifier is known from European Patent Application 598 585. In that Application, an input signal is preprocessed and split into two mutually orthogonal signal components (quadrature components). The two quadrature components are passed, in parallel, through associated signal paths of an error amplifier, after whey they are re-combined and up-converted to a RF band. The output signal of the amplifier is utilized to provide a feedback signal. This feedback signal is down-converted from the high-frequency band to the baseband and resolved into two quadrature components. These quadrature components are fed to respective inputs of the error amplifier. The preprocessor for the input signal is periodically switched into a calibration mode in which test signals are applied to the amplifier instead of the input signal. At these times the signal strength of the output signal of the power amplifier is measured and used to provide predistortion factors in the signal preprocessor to improve amplifier linearity.